Procede de fabrication d&#39;une piece de carrosserie de vehicule automobile, piece de carrosserie

ABSTRACT

The present invention relates to a method of fabricating a motor vehicle bodywork part comprising a metal sheet. The metal sheet is shaped after previously being coated with a surface covering suitable for acting as a mechanical bonding interface with a thermoplastic material. The invention also provides a bodywork part, in particular a fender, a door, or a tailgate.

The present invention relates to a method of fabricating a motor vehicle bodywork part, to a bodywork part, to a fender, to a door, and to a tailgate.

BACKGROUND OF THE INVENTION

In the automobile industry, it is known that it is advantageous to off-load as much work as possible from the main assembly line, and thus to develop modules that are already fitted out and ready for mounting. By way of example, such fitted modules can be bodywork parts having functional members of plastics material already fastened thereto, such as reinforcement, means for fastening the bodywork parts to the vehicle, spacers, or headlights.

Amongst the means for fastening such various functional members to the bodywork part, there are already known in the state of the art specific adhesives adapted to the sheet metal of the bodywork part.

The problem lies in that using adhesive between the various parts requires adhesive to be put into place in precise locations, and that is expensive in terms of labor. Furthermore, when it is desired to secure a part on a bodywork part that has already been stamped, certain zones are particularly difficult to reach, thus increasing the difficulty of preparing such fitted-out bodywork parts. In addition, if fastener means are used other than adhesive, then the bodywork part is weakened because of point connections.

OBJECTS AND SUMMARY OF THE INVENTION

The present invention seeks to remedy those drawbacks by proposing a method of fabricating a bodywork part whereby bonding functional members to the bodywork part by adhesive is made particularly easy and quick.

To this end, the invention provides a method of fabricating a motor vehicle 1 part comprising a metal sheet, wherein the metal sheet is shaped after prior coating with a surface covering capable of acting as a mechanical bonding interface with a thermoplastic material.

Thus, such a method makes it possible to obtain a shaped bodywork part that already carries a layer of adhesive. Since the entire metal part is coated, operators have no need to apply adhesive for each member that is subsequently to be fastened onto the bodywork part.

In addition, the surface covering coated on the sheet makes it possible to protect the part or a portion of said part against corrosion.

In an implementation, the surface covering is constituted by a material that is reactivatable, preferably by applying heat. Thus, the material reacts only above a certain temperature, such as the temperature at which the thermoplastic material of the member is injected, thereby enabling the metal sheet to be shaped without the surface covering becoming bonded to the shaping tools.

Once the pre-coated bodywork part has been shaped, thermoplastic material constituting a member can be applied thereto in two ways. Either the thermoplastic material for constituting a member is overmolded onto the pre-coated sheet, with the surface covering then acting as a bonding interface. Otherwise, the surface covering is reactivated and a member made of a thermoplastic material is applied thereto with the surface covering acting as a bonding interface.

In a preferred implementation, an area of the metal sheet coated with the surface covering is not covered by the member made of thermoplastic material, and is referred to as a free area. This free area can serve as a bonding interface for some component other than the member. Thus, by reactivating the free area anew, it is possible to cause it to react in such a manner that the surface covering can act as fastener means for some other element.

Optionally, a member is used that is selected from at least one of the elements in the group constituted by: a lining, fastener means, reinforcing means, a soundproofing screen, means for docking the bodywork part, and a spacer. Thus, the method defined by the invention makes it easy to hold in place: reinforcement, e.g. against vibration, noise, or heat; or fastener means for fastening the bodywork part to the vehicle, or a headlight to the bodywork part; all of which members can be fastened to the bodywork part at lower weight and lower cost.

In a first implementation, the prior coating of the metal sheet with the surface covering is performed immediately after the metal sheet has itself been fabricated, e.g. in the form of sheet metal. The pre-coated sheet metal is subsequently shaped, and the thermoplastic material of the member is applied to the shaped and pre-coated sheet metal in accordance with the invention.

In a second implementation, the prior coating of the metal sheet is performed immediately before the metal sheet is shaped. A method of the invention may further comprise one or more of the following characteristics:

-   -   using a substance that is compatible with the plastics material         of the member as the surface covering;     -   using a plastics material for the member that includes a         substance in common with the surface covering coated on the         metal sheet;     -   encouraging bonding of the member on the surface covering by         using a metal sheet having a surface covering comprising a         binder, the covering itself being covered on its face remote         from the metal sheet with a film of thermoplastic material made         of the same material as the member;     -   making the overmolded or applied member out of polypropylene or         polyamide;     -   ensuring that the surface covering coated on the metal sheet         includes polypropylene or polyamide; and     -   performing a step of folding or stamping in order to shape the         metal sheet.

The present invention also provides a motor vehicle bodywork part obtained by implementing a method as defined above.

The bodywork part may be a fender, a door, a tailgate, a hood, or a roof.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be better understood on reading the following description given purely by way of example and made with reference to the accompanying figures, in which:

FIG. 1 is an inside view of a motor vehicle fender in accordance with the invention;

FIG. 2 is a section view of a motor vehicle fender in a second embodiment of the invention;

FIG. 3 is a front perspective view of a motor vehicle fender in a third embodiment of the invention; and

FIG. 4 is a section of a motor vehicle fender in a fourth embodiment.

MORE DETAILED DESCRIPTION

The bodywork part 10 shown in FIG. 1 is a motor vehicle front fender. The fender 10 comprises a metal sheet 12 made by stamping sheet metal.

On its inside surface, the fender 10 further comprises an example of a member of the invention, constituted in this case by a functional member 13 providing central reinforcement against vibration and noise, and made of a thermoplastic material such as polypropylene.

In order to bond the metal sheet 12 and the functional member 13 together, the sheet is covered with a surface covering 16 acting as a mechanical bonding interface with the reinforcement 13.

The surface covering 16 also serves to provide the bodywork part 10 with anticorrosion protection, in full or in part.

The surface covering 16 is made of a material which presents the following characteristics:

-   -   it is thermoreactive, i.e. it acquires adhesive properties at a         certain temperature;     -   it is suitable for bonding to metals, like the adhesives known         in the prior art for bonding together metal structural parts         such as a hood with a hood liner, or a tailgate with a tailgate         liner, and as sold in particular by the supplier Henkle; and     -   it contains polypropylene.

The metal sheet 12 and the reinforcement 13 are assembled together as follows.

In a first step, at least the entire inside surface of the metal sheet is pre-coated with the surface covering 16. This first step is performed as soon as the sheet metal has been fabricated, prior to it being sold.

In a second step, the sheet 12 pre-coated in the covering 16 is cut and shaped by stamping or folding so as to take on the shape shown in FIG. 1.

In a third step, the sheet metal as prepared in this way is placed in a mold into which polypropylene is injected so as to form the reinforcement 13.

While this overmolding operation is taking place, the polypropylene is injected at a temperature that is relatively high so as to ensure that it is liquid. This temperature is also high enough to cause the material constituting the interface layer 16 to react.

Furthermore, since the material of the structure covering 16 includes polypropylene, it is compatible with the polypropylene that is injected to mold the reinforcement 13.

Consequently, when the polypropylene comes into contact inside the mold with the surface covering 16, the covering reacts so as to establish a bond between the reinforcement 13 and the metal sheet 12.

As can be seen on the fender of FIG. 1, after injection, a bodywork part is obtained in which the interface layer 16 and the injected thermoplastic material have melted so as to provide a continuous bond between the plastics material of the reinforcement 13 and the metal sheet 12.

Optionally, in an implementation not shown, the surface covering 16 is itself covered, prior to overmolding, by a film of polypropylene, so as to enhance bonding with the polypropylene constituting the functional member 13.

It can be seen that since the sheet 12 is pre-coated over the entire area of the covering 16, certain zones 20 that are not covered with plastics material during the injection molding operation do not react and are not covered with the plastics material. Consequently, these areas 20 that have remained free and that include the surface covering 16 can be reactivated subsequently by applying heat so as to make it possible to fasten other components to the bodywork part 12.

The functional member 13 shown in FIG. 1 is a piece of central reinforcement against vibration and noise. Nevertheless, it is possible to apply other types of members to the fender 10. The member may constitute means for fastening a separate part applied to the fender 10; internal reinforcing means, possibly ribs, against vibration, noise, or heat; a screen against sound or heat; means for docking the fender 10 with some other bodywork part, for example a wheel arch or a bumper; spacer means, optionally fusible spacer means, for controlling bodywork clearances; means for positioning a headlight glass relative to the bodywork part; or indeed means for fastening a headlight to the bodywork part.

Examples of functional members can be seen in FIGS. 2 to 4.

In FIG. 2, the fender 10 comprises docking means 22 for a wheel arch, and fastener means 24 for fastening the top of the fender to the structure of the vehicle so that the fender 10 is put into a reference position relative to the vehicle hood.

In FIG. 3, it can be seen that the front portion of the fender 10 that is to come into contact with the vehicle headlight includes means 26 for putting a headlight into a reference position relative to the fender 10, docking means 28 for engaging the bumper relative to the fender 10, and fastener means 30 for fastening the fender 10 to the vehicle structure.

Finally, in FIG. 4, it can be seen that the fender 10 may include fastener means for engaging a front pillar of the vehicle, so as to bring into alignment with a front door of the vehicle.

Thus, by means of the invention, it is easy by reactivation the surface covering 16 to apply elements to the inside of the fender 10 without it being necessary to take care in positioning adhesive specifically for each applied member.

In addition to greatly simplifying the steps of shaping the bodywork part made in this way, a method of the invention has the advantage of reducing the cost of fabricating the part. Since functional members made of plastics material can be applied easily, the metal sheet 12 of the bodywork part performs essentially an esthetic function, giving an impression of quality, strength, and an appearance that is specific to metal. Consequently, the prepared module comprising the bodywork part and its members is lighter in weight and also less expensive since the plastics material used is functional and does not contribute to appearance, so it is therefore less specific and less expensive.

In addition, a single part can be obtained in the form of a fender provided with docking means and reinforcing means improving stiffness thereon and on which it is easy to integrate other functions, while nevertheless reducing the overall weight of the fitted bodywork part.

Finally, it should be observed that the invention is not limited to the embodiments descried above. 

1. A method of fabricating a motor vehicle bodywork part comprising a metal sheet, wherein the metal sheet is shaped after prior coating with a surface covering capable of acting as a mechanical bonding interface with a thermoplastic material.
 2. A method according to claim 1, in which a reactivatable material is used as the surface covering.
 3. A method according to claim 1, in which a thermoplastic material is overmolded onto the pre-coated sheet so that the surface covering acts as a bonding interface, which thermoplastic material serves to constitute a member.
 4. A method according to claim 2, in which the surface covering is reactivated and a member made of a thermoplastic material is applied thereto with the surface covering acting as a bonding interface.
 5. A method according to claim 3, in which a substance that is compatible with the plastics material of the member is used as the surface covering.
 6. A method according to claim 5, in which the member is made of a plastics material having a substance in common with the surface covering coated on the metal sheet.
 7. A method according to claim 3, in which bonding between the member and the surface covering is enhanced by using a metal sheet having a surface covering comprising a binder, said covering being covered on its face remote from the metal sheet with a film of thermoplastics material made of the same material as the member.
 8. A method according to claim 3, in which the overmolded member comprises a material selected from a group consisting of polypropylene and polyamide.
 9. A method according to claim 3, in which an area of metal sheet coated in the surface covering is not covered by the member of thermoplastic material, and is referred to as a free area.
 10. A method according to claim 9, in which the free area acts as a bonding interface with a component other than the member.
 11. A method according to claim 3, in which the member is selected from at least one of the elements in the group consisting of a liner; fastener means; reinforcing means; a noise screen; docking means for the bodywork part; and a spacer.
 12. A method according to claim 1, in which the metal sheet is coated with the surface covering as soon as the metal sheet is fabricated.
 13. A method according to claim 1, in which the metal sheet is coated with the surface covering immediately prior to the metal sheet being shaped.
 14. A method according to claim 1, in which the surface covering coated on the metal sheet includes a material selected from a group consisting of polypropylene and polyamide.
 15. A method according to claim 1, in which the shaping of the metal sheet includes a step of folding or stamping.
 16. A motor vehicle bodywork part comprising a metal sheet and fabricated by shaping the metal sheet after prior coating with a surface covering capable of acting as a mechanical bonding interface with a thermoplastic material. 17-21. (canceled)
 22. The motor vehicle bodywork part of claim 16, wherein the bodywork part is selected from a group consisting of a door, a tailgate, a hood and a roof.
 23. A method according to claim 3, in which the applied member comprises a material selected from a group consisting of polypropylene and of polyamide. 